Instructions
Go to Cianwood City, and walk west until you enter the Safari Zone.
Unlock block items, if you haven't done so already, by bringing Warden Baoba a Sandshrew. When you do so, Baoba gives you a box of items to take with you into the Safari Zone areas.
Select the area you want to customize with block items on the touch screen. You are able to choose from six areas, such as forest, plains, mountain peaks or water.
Put the item in any desired place in the selected area. Some block items work better when placed in specific areas. For example, a mossy rock works best in the peaks area, and a fountain works best in the water area.
Wait for the desired Pokemon to appear. Look at the customization screen to see if any Pokemon are visiting an area.
Leave the block items in place for a number of days if the Pokemon you want isn't appearing. Pokemon tend to have a block item requirement. For instance, some Pokemon need 18 objects to appear, so if you have only two blocks placed, they won't come. As each day passes, though, block items increase in value. A block item that is worth only one block on its first day, therefore, may eventually be worth up to seven blocks.